Covering cakes with Fondant:

Tip # 1: "Crumb coat your cake smooth by lightly icing the cake with butter-cream icing. Any imperfections will show through the rolled fondant. Try to use white icing unless you are using a dark tinted fondant."

Remember:  Do not put to much icing, this will prevent the fondant to break and the cake will look smoother.  You can also use jam instead of butter-cream icing.